In a manufacturing process of an electric device such as a semiconductor device or a liquid crystal display device, there are performed a film forming process for forming a conductive film or an insulating film on the surface of a substrate, an etching process for etching a film formed on the substrate and the like.
For example, a plasma etching apparatus is widely employed in the etching process, wherein the plasma etching apparatus includes a processing chamber for accommodating therein a substrate. In the processing chamber, there are installed a lower electrode for mounting the substrate thereon and a shower head, also serving as an upper electrode, for injecting a gas onto the substrate mounted on the lower electrode. In the etching process, while a specified gaseous mixture is injected through the shower head, a radio frequency power is applied between the electrodes. Accordingly, a plasma is generated in the processing chamber and a film formed on the substrate is etched by the plasma.
However, etching characteristics such as an etching rate and an etching selectivity are influenced by a concentration of a gas supplied onto the substrate. Further, conventionally, it has been a major challenge to improve a uniformity of etching in the surface of the substrate by making the etching characteristics uniform on the surface of the substrate. Thus, there is proposed a technique of dividing an inner space of the shower head into a plurality of gas chambers, wherein each gas chamber is independently connected to an individual gas introduction line such that a gaseous mixture containing gases whose kinds and flow rates are optionally chosen based on the necessity can be supplied to each portion in the surface of the substrate (see, e.g., Reference 1). Consequently, a partial gas concentration on a small part in the surface of the substrate can be locally controlled to thereby improve an etching uniformity on the surface of the substrate.
However, the gaseous mixture for use in the etching process contains various gases, for example, an etching gas, a gas for controlling deposits of reaction products, a carrier gas such as an inert gas, that are chosen depending on a material to be etched, process conditions and the like. Accordingly, for example, when an inner space of the shower head is divided into a plurality of gas chambers and a gas introduction line is independently connected to each of the gas chambers, as shown in FIG. 1 of Reference 2, each gas introduction line is connected to lines communicating with multiple gas supply sources and, further, a mass flow controller is provided in each line. Thus, a piping structure of a gas supply system becomes complicated and a control of gas flow rate is also complicated in each line. Therefore, for example, a large piping space is required, which in turn increases the expense of an apparatus control system.    [Reference 1] Japanese Patent Laid-open Application No. 8-158072    [Reference 2] Japanese Patent Laid-open Application No. 9-45624